Until late in the nineteenth century, the processing of cereals was essentially the same as that used in Biblical times, namely grinding between stones. With the introduction of modern roller mills, the physical and chemical properties of the cereal grain became important, and fractions of the cereal grains became available for special uses. Chemists were called on to determine the composition of these fractions, to establish specifications for those most useful, and to devise processes leading to better cereal products.
Through the years different processes for preparing ready-to-eat cereal products have evolved. Today, the process selected by a manufacture would depend on the end product desired. The manufacture of ready-to-eat cereal by the major manufacturers has been restricted to about three processes. For instance, if a flaked cereal is desired, the manufacturing steps required are as follows: Batch cooked--The cereal materials are cooked in a rotary steam cooker. The cooked product is discharged and broken into small pieces or grits which are dried and flaked; Continuous cooked--The rotary steam cooker is replaced by a steam locked auger wherein the product is cooked under steam as it passes through the auger. The material is discharged as grits, or can pass into a sizer or former then flaked or shredded in other cereal forms; Utilization of an Extruder--The cooked cereal matrix passes into an extruder and is formed into a desired shape and form. The cereal forms mention above can also be gun puffed into an expanded cereal.
Extruders have been used for the preparation of ready-to-eat cereal products. However, it has been generally used for the preparation of expanded or puffed cereals in an attempt to replace the somewhat antiquated gun puffing process. Extruders are also being used as cookers and formers, particularly in the pet food industry. One of the major drawbacks of the use of extruders in the manufacture of ready-to-eat cereal products is the uncooked or undeveloped cereal flavor profile which results from the short residence time within the extruder which does not permit the desired physical and biochemical reactions which are necessary to develop an acceptable flavor profile. Almost as important as the ability to develop flavor is the development of acceptable color which is unattainable because of the short residence time within the extruder.
Another effect of the limited residence time within the extruder is the extremely high temperatures that are most often utilized, which generally cause undesired degradation of the formula components particularly in the cereal manufacture. These high temperatures result in spontaneous expansion within the food product due to the release of steam as the food drops to atmosphere pressure as it exits the extruder through the die. While desirable in expanded products (puffed), this expansion can have an undesirable effect on the more dense cereal products.
The use of a post extrusion tube fitted at the distal end of an extruder to accomplish a universal process for the manufacture of substantially all types of cereal products have not been accomplished to date. A tubular attachment, however, has been used to incorporate additives into extruded food products. For instance, U.S. Pat. No. 4,454,804 by McCulloch discloses a cylindrical bore attachment to the external face of the extruder die plate which has the same cross-sectional area and shape as the die orifice of the extruder. As the product passes through the die into the cylindrical bore while under pressure, one or more liquid additives are injected under pressure into the body of the extrudate. As the extrudate exits the cylindrical bore it expands to form a porous structure.
U.S. Pat. No. 3,496,858 by Jenkins discloses an extension tube attached at the die face wherein the extrudate passes into the extrusion tube attachment as it exits the extruder for further texturization. The extension tube has a diameter similar to that of the die orifice. However, temperature and pressure within the tube is normally atmospheric which allows for some expansion. Also, the presence of a die plate restricts the outlet of the product. Further, U.S. Pat. No. 3,861,287 by Menser discloses an apparatus containing a cooking feed screw and a cooling feed screw. The material being treated may be expelled prior to entering the cooling feed screw or it may be routed through the cooling feed screw for further treatment.
U.S. Pat. No. 4,128,051 by Hildebolt discloses a confined treatment zone in communication with the extrusion die wherein the extruded protein material passes and is subjected to steam which further texturizes the protein.
The above references disclose a variety of post extrusion treatments. These treatments generally occur within a tubular attachment adjacent to the die plate. Further, none of the references are directed to the production of a ready-to-eat cereal product, or a process for preparing same. The tubular extensions are either directed to enhance texturization of vegetable protein products or to produce dual textured product.
The output performance of an extruder is generally dependent upon the effectiveness of solids conveyance within the extruder. It has been found that the frictional properties of an extruder wall have a direct and important effect on how efficiently the material will be moved through the extruder and hence will affect the output of the extruder. In the case of a post extrusion tube or attachment tube, none of the references disclose an interior lining for the purpose of reducing friction within the tube. However, U.S. Pat. No. 4,309,115 by Klein et al, discloses changing the coefficient of friction within a plasticating extruder to improve solids conveyance by coating the inner surface of the extruder barrel with a special material.
It is, therefore, an object of the present invention to provide a single process and apparatus adaptable for the preparation of most farinaceous products.
Another object of the present invention is to provide a single process and apparatus adaptable for the preparation of a cereal product.
A further object of the present invention is to provide a process and apparatus adaptable for the preparation of a flaked cereal product.
Yet another object of the present invention is to provide a process and apparatus adaptable for the preparation of a puffed cereal product.
Still a further object of the present invention is to provide a process and apparatus for the preparation of a cereal grit.